CO2 Adsorption Behavior Research Articles

Molecular simulation of adsorption and diffusion behavior of CO2 in pyrophyllite

Understanding the microscopic process of adsorption and diffusion of CO2 in clay minerals is important for geological storage of CO2. In this study, Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) simulations are used to obtain the adsorption and diffusion behavior of CO2 in pyrophyllite slit pores. The influence of split pore size, temperature, pressure, and water content were analyzed in detail. The adsorption characteristics of CO2 in pyrophyllite were revealed by discussing the distribution of CO2 density profile, adsorption capacity, isosteric heat of adsorption, interaction energy, mean square displacement, self-diffusion coefficient, and molecular orientation distribution. It shows that the excess adsorption isotherm of CO2 in pyrophyllite slit pores demonstrate significant supercritical adsorption characteristics. Surface attractions originating from both pore walls overlap in the middle of pore, leading to an enhanced adsorption capacity of CO2 in pyrophyllite slit pores when pore aperture is lower than 3 nm. In pyrophyllite pores, the presence of water has an enhancing effect on CO2 adsorption when the water content is below 30 wt%. A maximum value of CO2 adsorption amount is reached at the water content of 10 wt%, while negative growth occurs at 35 wt%. At low water content, water molecules form a weak adsorption layer due to the weak attraction of pyrophyllite to water. As water content increases, the self-diffusion coefficient of the CO2 decreases, and the diffusion capacity decreases. The adsorption state of the CO2 molecule on the mineral surface is primarily a parallel configuration, while the water molecule has no clear orientation. Our calculated results can provide guidance for further study of clay-water-adsorbate interface reaction of hydrophobic minerals.

Development of CO2 adsorption materials from recycling spent tire char via orthogonal design: Optimal solution and thermodynamic evaluation

This work uses chemical-physical activation to upgrade spent tire char for capturing CO2, and CO2 gas flow rate is the dominant factor of activation process based on the orthogonal experimental design. The final spent tire activated carbon with a specific surface area of 762.17 m2/g and a microporous pore volume of 0.23 cm3/g was obtained. The CO2 adsorption behavior can be described by the Langmuir and Freundlich models. The optimum spent tire-based activated carbon has the capacity to capture CO2 up to 1.42 mmol/g. It was also confirmed by Gibbs free energy change studies that the optimum spent tire-based activated carbon at less than 58.77 °C allows the CO2 adsorption reaction to proceed spontaneously. The excellent regenerability of the produced activated carbon material was demonstrated by the isosteric heat of adsorption. The process of CO2 adsorption was also confirmed as physical adsorption by various thermodynamic means. The spent tires recycling as CO2 adsorbent is a promising path which realizes the dual benefits of waste recycling and CO2 reduction.

Mechanism exploration of surface functional groups and pore sizes on CO2 adsorptive separation by GCMC and DFT simulations

The purpose of this study is to analyze the mechanistic effect of surface functional groups and pore sizes of graphene on the CO2 adsorption and separation behaviors by grand canonical Monte Carlo (GCMC) simulation and density functional theory (DFT) calculation. For the surface functional groups, the M−doped (M = N, P, S, O) functionalized graphene materials (G-Rs) exhibit a higher CO2/N2, CO2/H2 and CO2/CH4 adsorption selectivity than pristine graphene (G-None) in the entire pressure range. Especially, due to a stronger electrostatic interaction, the P-doped functionalized graphene materials (P-G-Rs) present the best CO2 separation performance. For the pore size, the influence of pore size on the CO2 adsorptive separation process depends on pressure ranges. At low pressures, 0.8 nm pore shows the highest CO2 adsorption selectivity. However, as for high pressure, the actual pore volume plays the dominant role. Furthermore, by analyzing the isosurface maps of electrostatic potential and van der Waals (vdW) potential, we conclude that the electrostatic effect determines the optimal adsorption sites for polar gas molecules (CO2) rather than non-polar molecules (N2, H2 and CH4), while the vdW interaction plays a secondary role in the intermolecular interaction. This study provides a novel theoretical guidance in designing and preparing modified graphene for CO2/other gas molecules mixture separation.

Controlling Diels-Alder reactions in catalytic pyrolysis of sawdust and polypropylene by coupling CO2 atmosphere and Fe-modified zeolite for enhanced light aromatics production

Producing value-added light aromatics (BTEX) from solid waste streams holds excellent promise for resource recovery. Here we present a thermochemical conversion approach that enhanced BTEX production by coupling CO2 atmosphere and Fe-modified HZSM-5 zeolite to facilitate the Diels-Alder reactions in catalytic pyrolysis of sawdust and polypropylene. The Diels-Alder reactions between sawdust-derived furans and polypropylene-derived olefins could be controlled by tuning CO2 concentration and Fe loading amount. Sufficient CO2 (≥50%) with moderate Fe loading (10 wt%) were observed to produce more BTEX and fewer heavy fractions (C9+aromatics). To deepen the mechanistic understanding, quantification of polycyclic aromatic hydrocarbons (PAHs) and catalyst coke was further conducted. The co-use of CO2 atmosphere and Fe modification suppressed the appearance of low-, medium-, and high-membered ring PAHs by over 40%, decreased pyrolysis oil toxicity from 42.1 to 12.8 μg/goil TEQ, and transformed coke from "hard" to "soft". Based on the characterization of CO2 adsorption behavior, it was deduced that the introduced CO2 was activated by loaded Fe and reacted in situ with H2 generated during aromatization to expedite H-transfer. Meanwhile, BTEX recondensation was prevented through the Boudouard reactions of CO2 and water-gas reactions between the resulting water and carbon deposits. These synergistically enhanced the production of BTEX and suppressed the formation of heavy species, including PAHs and catalyst coke.

Enrichment of carbon dioxide using Mg–Al layered double hydroxides

Owing to the low atmospheric concentration of CO2 (400 ppm), direct air capture technologies require adsorbents that offer high CO2 adsorption capacities at low CO2 concentrations. In this study, we investigated the potential of CO3·Mg–Al layered double hydroxides (LDHs; Mg/Al molar ratio = 2, 3, and 4) as CO2 adsorbents. The CO2 adsorption and desorption behavior was studied at various molar ratios, adsorption/desorption temperatures, and linear speeds. CO2 adsorption by CO3·Mg–Al LDH followed the Langmuir model, indicating that monolayer adsorption occurs. The maximum CO2 adsorption quantity calculated using the Langmuir equation was 0.794 mmol/g for CO3·Mg–Al LDH with a Mg/Al molar ratio of 3. In dry CO2 adsorption experiments, a maximum CO2 adsorption quantity of 0.319 mmol/g was recorded with a Mg/Al molar ratio of 3 and temperature of 60 °C. In dry CO2 desorption experiments, the CO2 concentration and desorption quantity reached maximum values at 300 °C and a linear speed of 0.250 m/min. Notably, the maximum CO2 concentration was 6232 ppm, showing a 15.6-fold increase in comparison with the initial concentration of 400 ppm. Overall, our results demonstrate that CO3·Mg–Al LDH has high potential as a CO2 adsorbent. The study findings have significant implications for the development of new CO2 adsorbents for the direct air capture and storage of CO2.

Molecular interactions of CO2 and CH4 and their adsorption behaviour in kerogens with different grades of maturity

ABSTRACT CO2 sequestration (CS) into the shale formations can reduce not only carbon emissions but also enhance gas recovery (EGR). The adsorption and diffusion behaviour of CO2 and CH4 on kerogens with different maturity play a crucial role in CS-EGR as they determine the efficiency of CO2 storage and energy recovery. In this work, GCMC and MD simulations were performed to investigate the adsorption and diffusion behaviour of CO2 and CH4 on kerogen models at different grades of maturity. It indicated that, in the same maturity, the CO2 adsorption capacity was more significant than that of CH4. With increasing maturity, the adsorption capacity and diffusion rate increased. With the increase of water contents, the swelling ratio of kerogens increased, and the adsorption capacity and the diffusion coefficients of CH4 and CO2 decreased. However, the adsorption selectivity of CO2 over CH4 significantly increased. H2O and CO2 molecules both preferred to adsorb on functional groups of oxygen, nitrogen and sulfur. This study consolidated our hypothesis that an injected CO2 to shale gas and oil formations contributed positively to enhanced energy recovery owing to the difference in adsorption and diffusion behaviour of CH4 and CO2 in kerogens with different maturity in gas and oil reservoirs.

Relevance of Surface Adsorption and Aqueous Complexation for the Separation of Co(II), Ni(II), and Fe(III)

During the solvent extraction of metal ions from an aqueous to an organic phase, organic-soluble extractants selectively target aqueous-soluble ions for transport into the organic phase. In the case of extractants that are also soluble in the aqueous phase, our recent studies of lanthanide ion-extractant complexes at the surface of aqueous solutions suggested that ion-extractant complexation in the aqueous phase can hinder the solvent extraction process. Here, we investigate a similar phenomenon relevant to the separation of Co(II), Ni(II), and Fe(III). X-ray fluorescence near total reflection and tensiometry are used to characterize ion adsorption behavior at the surface of aqueous solutions containing water-soluble extractants, either bis(2-ethylhexyl) phosphoric acid (HDEHP) or 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEHEHP), as well as adsorption to a monolayer of water-insoluble extractant dihexadecyl phosphoric acid (DHDP) at the aqueous-vapor interface. Competitive adsorption of Ni(II) and Fe(III) utilizing either HDEHP or DHDP illustrates the essential feature of the recent lanthanide studies that the ion, which is preferentially extracted in liquid-liquid extraction, Fe(III), is found preferentially adsorbed to the water-vapor interface only in the presence of the water-insoluble extractant DHDP. A more subtle competition produces comparable adsorption behavior of Co(II) and Ni(II) at the surfaces of both HDEHP- and HEHEHP-aqueous solutions in spite of the known preference for Co(II) under solvent extraction conditions. Comparison experiments with a monolayer of DHDP reveal that Co(II) is preferentially adsorbed to the surface. This preference for Co(II) is also supported by molecular dynamics simulations of the potential of mean force of ions interacting with the soluble extractants in water. These results highlight the possibility that complexation of extractants and ions in the aqueous phase can alter selectivity in the solvent extraction of critical elements.

Molecular simulation on CO2/H2S co-adsorption in organic and inorganic shale nanopores

Geological CO2 sequestration (GCS) in depleted shale reservoirs is recognized as one of promising techniques to mitigate CO2 emissions, while the high cost of CO2 purification greatly hinders its deployment. Co-injection of CO2/H2S mixtures has been proposed as an economical alternative to further promote GCS application. In this work, we used Grand Canonical Monte Carlo (GCMC) and molecular dynamic (MD) simulations to investigate CO2/H2S mixture adsorption in organic and inorganic shale nanopores (at 333.15 K and pressure up to 50 MPa). CO2 and H2S present distinct adsorption behaviors on the different surfaces. H2S adopts unordered structures on kerogen surfaces, but a perpendicular orientation on illite due to H-bonding, which also results in higher adsorption, while CO2 is preferentially distributed parallel along the surfaces. Furthermore, CO2 and H2S accumulate in the concave parts of kerogen surfaces, while they concentrate around the tetrahedral aluminum (AT) atoms and K+ cations on illite surfaces. The adsorption selectivity of H2S over CO2 is always greater than 1, indicating the stronger adsorption propensity of H2S. The preferential adsorption of H2S on illite surface is facilitated by the stronger dipole–dipole interactions. PMF results show that the binding interaction between CO2 or H2S and illite is higher than on kerogen, and H2S always shows a stronger interaction than CO2. Overall, the total CO2 and H2S adsorption is higher in illite nanopores, implying a new promising storage method. This study provides important insights into the competitive adsorption mechanisms of CO2 and H2S in depleted shale reservoirs and sheds light on how sour gas geological sequestration capacity can be further improved.

Adsorption of Co(II) from the simulated solution by zeolite NaX derived from rice husk ash

The adsorption of Co(II) from the simulated solution was investigated using zeolite NaX derived from rice husk ash as an alternative adsorbent. The adsorption behavior of Co(II) depended strongly on the equilibrium pH, Co (II) concentration, zeolite NaX dosage, and reaction time. The high adsorption efficiency of Co(II) by zeolite NaX was obtained under the conditions: pH 3.0, 100 mg/L of Co(II), 5 g/L of zeolite NaX, and a reaction time of 75 min. The loading behavior of Co(II) onto the zeolite NaX was well-fitted to the Freundlich adsorption isotherm and the Co(II) loading capacity by zeolite NaX was around 38 mg/g. The obtained results indicate that synthesized zeolite NaX from rice husk ash is a potential adsorbent to remove cobalt from waste solutions due to its high adsorption.

Zr3C2O2 MXene as promising candidate for NH3 sensor with high sensitivity and selectivity at room temperature

MXene materials have attracted extensive attention due to their graphene-like structures and promising future applications in many fields. The gas adsorption behavior of NH3, NO, H2S, N2, H2, O2 and CO on Zr3C2O2 are investigated by using first principles simulations. The calculated adsorption energies and charge transfers indicate that Zr3C2O2 could be a promising candidate as room-temperature NH3 gas sensing material due to its high selectivity, superb sensitivity and short recovery time. The factors influencing the gas sensing behavior of MXenes are analyzed. The results show that the gas sensing performance of MXenes can be modulated by altering the interaction between the gas molecules and the substrate through the surface functional group, transition metal, and the biaxial strains. This study could guide the feasibility of using monolayer Zr3C2O2 as NH3 gas sensor in further experimental applications and provide an effective way to tailor MXene series in compliance with various applications.

New insights into the co-adsorption behavior of H2O and H2 on defective PuH2 (100), (110), and (111) surfaces from first-principles study

Attack of hydrogen on plutonium is the key factor that causes plutonium corrosion. In this study, we explored the interfacial interactions of H2O and H2 molecules with the defective PuH2 (100), (110) and (111) surfaces through DFT + U approach. The adsorption energy results suggest that the H2O may be preponderant in competitive adsorption with H2. The OH group or O atom from H2O and H atom from H2 attempt to “heal” the vacancy. The co-adsorption study of multiple H2O molecules indicates that a mixed adsorption state of H2O molecules and OH groups was found near the defect. The dissociated H atoms in H2O molecules would recombine into new hydrogen. In order to clarify the hydrogenation mechanism of hydride surface exposed to the coexistence environment of H2O and H2, we further investigated the co-adsorption behavior of H2O and H2 molecules on surfaces. It is found that there is a synergistic effect between the coexistence molecules.

Support Pore Structure and Composition Strongly Influence the Direct Air Capture of CO2 on Supported Amines.

A variety of amine-impregnated porous solid sorbents for direct air capture (DAC) of CO2 have been developed, yet the effect of amine-solid support interactions on the CO2 adsorption behavior is still poorly understood. When tetraethylenepentamine (TEPA) is impregnated on two different supports, commercial γ-Al2O3 and MIL-101(Cr), they show different trends in CO2 sorption when the temperature (-20 to 25 °C) and humidity (0-70% RH) of the simulated air stream are varied. In situ IR spectroscopy is used to probe the mechanism of CO2 sorption on the two supported amine materials, with weak chemisorption (formation of carbamic acid) being the dominant pathway over MIL-101(Cr)-supported TEPA and strong chemisorption (formation of carbamate) occurring over γ-Al2O3-supported TEPA. Formation of both carbamic acid and carbamate species is enhanced over the supported TEPA materials under humid conditions, with the most significant enhancement observed at -20 °C. However, while equilibrium H2O sorption is high at cold temperatures (e.g., -20 °C), the effect of humidity on a practical cyclic DAC process is expected to be minimal due to slow H2O uptake kinetics. This work suggests that the CO2 capture mechanisms of impregnated amines can be controlled by adjusting the degree of amine-solid support interaction and that H2O adsorption behavior is strongly affected by the properties of the support materials. Thus, proper selection of solid support materials for amine impregnation will be important for achieving optimized DAC performance under varied deployment conditions, such as cold (e.g., -20 °C) or ambient temperature (e.g., 25 °C) operations.

Computational investigation on CO2 capturing capacity of N-doped and Na-decorated Graphdiyne

Graphdiyne (GDY) is a newly discovered member of the two-dimensional carbon allotropes that has been proposed as a material for carbon dioxide (CO2) capture and storage technology. The GDY structure is composed of several hybridized carbon atoms, and despite its superior electronic capabilities, modifying its structure can facilitate the advancement of its practical applications. This study considered, N-doping, Na-decoration, and their combinations as GDY modifications. The dispersion-corrected density functional theory (DFT-D2) approach was used to investigate the structural and electronic properties of the resultant adsorbents and their CO2 adsorption behavior. Among three different N-doped structures, substituting an N atom for the Carbon with hybridization of SP2-SP (CSP2-SP) produced the most stable N-doped GDY with Ecoh = −7.23 eV. Four different locations of GDY were decorated by Na atom, and the center of the H3 was identified as the most stable site with Eads = −3.804 eV. This site was also the most favorable for Na decorating of the N-doped GDY, with Eads = −3.347 eV. Moreover, the results indicated that when a single CO2 was adsorbed on the Na-decorated GDY, the adsorption energy was −0.432 eV, the highest value among the pristine and modified structures. However, evaluation of the maximum CO2 capturing capacity of the systems revealed that N-doped GDY could capture eleven CO2 molecules, ca. 68.92 wt%, which makes it a potential candidate for future CO2 capture, storage, detection, and removal applications.

Effects of X (X = H2S, SO2 and N2O) mole fractions on adsorption behavior and phase equilibrium properties of CO2 + X mixed gas hydrate

As a remedy for air pollution caused by flue gas, Hydrate Based Gas Separation (HBGS) technology is under development. Among many issues in HBGS, the prediction for the adsorption and dissociation conditions of hydrate and the impact from mixed gas on the formation of carbon dioxide hydrate are crucial to understand the sequestration and separation of CO2. In this work, the occupancy isotherms of the mixed systems of CO2 + H2S, CO2 + SO2 and CO2 + N2O with different mole fractions of H2S, SO2 and N2O in sI and sII hydrates are examined. The results show that X (H2S, SO2 and N2O) in flue gases can increase the absorption of mixed gas; CO2 + H2S in the sI and sII hydrates can be categorized as the one-site Langmuir type. The calculated abundance ratio of CO2 to X vary with the mole fraction of impurity gas and pressure, which provide the prerequisite information for prediction of gas recovery yield at different conditions during the CO2 + X gas separate process. The phase equilibria of clathrate hydrates of mixed gases are predicted and the hydration numbers are determined. The results show that the dissociation pressure of mixed hydrates decreases as the impurity gas mole fraction increases, indicating that SO2, H2S and N2O gases can all promote the formation of CO2 hydrate. Additionally, inspection indicates that the mixed flue gas can be efficiently separate by clathrate hydrate.

Revealing the Pore Size-Dependent Sorption Mechanism of Toluene and Cetane in Porous Carbon by Nuclear Magnetic Resonance.

The adsorption of contaminants by porous carbon has been extensively studied by conventional isotherm and kinetic methods. However, the co-adsorption behavior and sorption sites of multiple contaminants in different-sized pores remain unclear. Herein, the nuclear magnetic resonance (NMR) approach is performed to investigate the adsorption mechanism of toluene and cetane in the confined space of carbon at the molecular level. The ring current effect induces the variation in the NMR chemical shifts of in-pore adsorbed toluene and cetane, realizing the identification of pore-dependent adsorption sites for contaminant removal. Cetane has a slower adsorption kinetic but a higher binding energy than toluene, which could squeeze toluene from micropores to larger pores with increasing adsorption quantity. This leads to a stronger competitive adsorption effect in small micropores than in mesopores. Accordingly, hierarchical porous carbons are determined to be the most effective adsorbents for the adsorption of coexisting contaminants. This study not only provides an effective NMR method to reveal the adsorption mechanism in the confined space of porous carbon at the molecular level but also offers new insights into the pore size-dependent adsorption of activated carbon for petroleum contaminant treatment.

Theoretical exploration of Rh1/CeO2 catalysts with high performance using CO oxidation as a probe reaction

Rh1/CeO2 attracts much attention in single-atom catalysis due to its unique catalytic performance and maximum atomic efficiency. Since different possible structures of Rh1/CeO2 coexist in real catalysts, it is hard to discriminate their catalytic roles and reaction mechanism due to the difficulty of preparing pure modeling catalyst. To solve this difficult problem, the adsorption and reaction behaviors of CO and O2 on four modeling catalysts of Rh1/CeO2 were systematically investigated by using density functional theory calculation in this work. The catalytic role and CO oxidation mechanism on Rh1/CeO2 catalysts were elucidated. On Rh1/CeO2(111), CO reacts with adsorbed O2 via Eley-Rideal mechanism; and the rate-determined step of CO oxidation cycle is CO reaction with the rest O atom of O2 with a barrier of 0.99 eV. On Rh1/CeO2-δ(111), CO reacts with activated O2 via Langmuir-Hinshelwood mechanism and continue the oxidation cycle via Rh1/CeO2(111). On RhxCe1-xO2, CO directly reacts with surface oxygen without barrier to form RhxCe1-xO2-δ; while the barrier of CO oxidation cycle on RhxCe1-xO2-δ is 1.18 eV. Upon the discrimination of the catalytic roles of Rh1/CeO2 catalysts with different structures, several important insights into design and development of Rh1/CeO2 catalysts with high oxidation performance were proposed.

Molecular simulation of thermodynamic properties of CH4 and CO2 adsorption under different moisture content and pore size conditions

In order to further clarify the thermodynamic properties of CH4 and CO2 adsorption in coal, a Monte Carlo method with a giant regular system was used to simulate the adsorption behavior of CH4 and CO2 in coal at different moisture contents and pore sizes. The results show that the adsorption of CH4 and CO2 in coal molecules is negatively correlated with the moisture content. As the pore size increases, the wall superimposed effect decreases, the stability of adsorption becomes less stable, and the selectivity of CO2 adsorption decreases, but the space to accommodate gas molecules becomes larger, which makes the adsorption amount rise. The average heat of adsorption of CH4 and CO2 showed a decreasing and then increasing relationship with the moisture content, and a negative correlation with the pore size, and the effect of H2O on CO2 is stronger than that of CH4. With the increase of moisture content, the absolute value of adsorption energy increases overall, and the high potential of water clusters tends to attract CO2 molecules more. With the increase of pore size, the wall superimposed effect weakens and the adsorption stability becomes worse, which makes the absolute value of adsorption energy smaller. The overall adsorption entropy of CH4 and CO2 has a negative correlation with moisture content and a positive correlation with pore size. The comparison of the slope of the fitted curves of adsorption entropy at different moisture contents adds that CO2 mainly displaces CH4 molecules in the middle of the pores at 3% moisture content.

Effect of binder on CO2, CH4, and N2 adsorption behavior, structural properties, and diffusion coefficients on extruded zeolite 13X

The effect of inorganic binder-based extrusion (Silica sol, Bentonite, Attapulgite, and SB1) in the selective adsorption of CO2, CH4, and N2 on zeolite 13X in the context of flue gas carbon capture and natural gas purification has been studied to reduce CO2 emissions. The effect of extrusion with binders was examined by adding 20 wt% of the mentioned binders to pristine zeolite and the results were analyzed by four approaches; (i) the effect on structural properties was analyzed by XRD patterns followed by Williamson–Hall (W–H) plot, FESEM images, and BET surface area. In addition, the mechanical strength of the shaped zeolites was measured by crush resistance testing; (ii) the effect on the adsorption capacity for CO2, CH4, and N2 were measured by volumetric apparatus up to 100 kPa; (iii) the impact on binary separation (CO2/CH4 and CO2/N2) were investigated; (iv) the influence on diffusion coefficients were estimated by micropore and macropore kinetic model. The results showed that the presence of a binder can cause reductions in BET surface area and pore volume, indicating partial pore blockage. It was found that the Sips model had the best adaptability to the experimental isotherms data. The trend of CO2 adsorption was 13X > pseudo-boehmite > bentonite > attapulgite > silica, in which the adsorption capacity reached 6.02, 5.60, 5.24, 5.00, and 4.71 mmol/g, respectively. Among all samples, silica was found the most suitable binder for CO2 capture in terms of selectivity, mechanical stability, and diffusion coefficients.

Zeolites as Selective Adsorbents for CO2 Separation

Zeolites are a very versatile class of materials that can display selective CO2 adsorption behavior and thus find applications in carbon capture, storage, and utilization (CCSU). In this contribution, the properties of zeolites as CO2 adsorbents are reviewed by critically presenting and discussing their assets and limitations. For this purpose, we first provide an overview of the CO2 adsorption mechanisms on different types of zeolites. Then, we systematically discuss the relationship between the physicochemical properties of zeolites (framework type, Si/Al ratio, and extra-framework cations) and their performance as CO2 adsorbents for the separation of CO2/CH4 (biogas) and CO2/N2 (flue gas) mixtures. Based on the trends and properties identified, we provide a comparison of the different zeolites and highlight their advantages and drawbacks for applicability in CO2 adsorption. Finally, we present the state of the art in the shaping of zeolites in macroscopic format, which is a key step toward their industrial utilization as adsorbents.

New insight into adsorption and co-adsorption of chlortetracycline hydrochloride and ciprofloxacin hydrochloride by Ga-based metal-organic gel/sodium alginate composite beads

Due to the extensive usage of tetracyclines and fluoroquinolones for disease control, their residuals usually coexist in wastewater and seriously affect human health and the entire ecosystem. To mitigate this problem, developing efficient and recyclable absorbent has been urgently required to be put on the agenda. In this research, Ga-based MOGs (GMOGs) were synthesized to remove chlortetracycline hydrochloride (CTC) and ciprofloxacin hydrochloride (CIP) in aqueous solution, followed by incorporating GMOGs into low-cost sodium alginate (SA) matrix to gain GMOG/SA beads with enhanced adsorption property, fine recycling performance and stable reusability. In single system (S-system), the adsorption behaviors of CTC/CIP by GMOGs and GMOG/SA beads including key operating factors, kinetics, isotherms and practicability were investigated systematically, and the maximum adsorption capacities for CTC/CIP by GMOGs and GMOG/SA beads achieved 406.50/158.23 mg g−1 and 1085.19/862.07 mg g−1, respectively. Furthermore, the proposed adsorption mechanisms were discussed. In binary system (B-system), regardless of suppressed co-adsorption behaviors of CTC/CIP by GMOGs and GMOG/SA beads arising from the competitive effect between CTC and CIP, their adsorption capacities still reached 207.90/126.90 mg g−1 and 588.24/571.42 mg g−1, respectively. Moreover, the value of industrial application was evaluated by testing the adsorption performance of GMOG/SA beads in bead columns and real water. This work provides a potential practicable, effective and recycled exploration of GMOG/SA beads for remediating the CTC and CIP co-contaminated wastewater.